1. Field of the Invention
This invention relates to belt conveyors and especially to belt conveyors having digging means on the outer surface thereof which impose radial, longitudinal, and lateral loads on the belt as it passes around the end pulleys and also in some applications on the straight length between pulleys.
2. Prior Art
Conveyors in the form of bucket ladders are commonly used in lifting bulk materials and are often used as diggers which are advanced into or across a pile or storage chamber to reclaim such material. Typically, such conveyors comprise a series of buckets which are secured at spaced intervals along endless chains which are constrained to a loop by sprocket wheels. The teeth of the sprocket wheels resist any side loads imposed on the buckets as the conveyor advances into the material at an angle to its longitudinal axis. Tension in the chains or the weight thereof, depending upon the arrangement, resists the tendency of the digging forces to lift the chains off of the sprockets.
Chain type bucket ladders are very heavy and cumbersome, however, and require very substantial supporting structures. This is a particular problem in reclaimers used to recover material from very large piles and in continuous ship unloaders where the bucket ladder is mounted on the end of a very long boom. In addition, chain type bucket ladders operate at relatively slow speeds.
A belt type conveyor fitted with buckets is much lighter and less cumbersome than a chain type bucket ladder, however, as is well known, belts tend to creep axially along end pulleys even when no intentional side loads are imposed on the conveyor. Where such a conveyor is fed into a pile with a component of motion lateral to the plane of the belt loop, very significant side loads are generated which must be resisted. In addition, at the digging end, the radially outward digging force tends to pull the belt away from the end pulley causing rapid deterioration of the belt.
As will be discussed in detail, the present invention employs one or more separate and independent wire ropes inside the loop of the endless belt as part of an arrangement to resist these radial and lateral forces. Wire ropes, of course, have been imbedded in conveyor belts to increase their tensile strength which aids in resisting the radial digging forces but this in itself does nothing to resist the lateral forces. Separate wire ropes have also been used inside the loops of endless belts to sustain the tensile load. In a great many of these, as exemplified for instance, by U.S. Pat. No. 2,751,065, the belt is frictionally supported on wire ropes on the level or on relatively shallow angled work runs, but is separated from the wire ropes at the end of the work run and goes around its own end pulley while the wire ropes are reeved through a separate arrangement of pulleys which applies driving tension to them. U.S. Pat. No. 2,747,726 discloses a belt conveyor in which wire ropes which separate from the belt at the end pulleys are mechanically gripped on the work and return runs by clamps attached to the belt. The conveyor in U.S. Pat. No. 3,388,786 comprises a series of rigid plates which slide with respect to one another and resilient linkages between plates which accommodate for changes in plate pitch at the end pulleys. The plates have curved bottoms conforming to the curvature of the end pulleys to facilitate cleaning of the plates as they travel around the end pulleys. The wire ropes on which the plates are supported on the work and return run are diverted around separate end pulleys.
In one prior art arrangement, a wire rope is coupled to the vertical portion of a belt type conveyor with integral pockets for holding bulk material by two rows of resilient blocks secured to the inside of the belt. The wire rope is forced into half round grooves in confronting faces of the blocks by a pulley at the beginning of the vertical run and is gripped tightly by pairs of pulleys spaced along the vertical run which urge the blocks toward each other with the wire rope inbetween. At the top of the vertical run, the blocks are received in a square cut peripheral groove in the deflection pulley and the wire rope is pulled out from between the resilient blocks as the belt, with the blocks attached, is deflected 90.degree. from the vertical to the horizontal while the wire rope continues 180.degree. around the pulley and proceeds vertically downward.
In these prior art arrangements, the wire rope is used to carry at least some of the tension forces imposed on the belt on the work run. The wire rope is either separated physically from the belt at the end pulleys or is otherwise decoupled from the belt in this area.
It is an object of the present invention to provide a rugged, light weight, high speed belt conveyor fitted with buckets or other digging means which can dig bulk material under conditions which impose high radial and/or lateral forces on the conveyor belt.
It is a more specific object of the invention to achieve the above objective using one or more wire ropes which are coupled to the conveyor belt only at the end pulleys.